Exploration of outer space requires efficient utilization of propellants that power exploration vehicles. An inherent limitation on a range of potential exploration is the mass of propellants an exploration vehicle must store onboard the vehicle to travel throughout that range: the greater the desired range, the greater the mass of onboard stored propellants, and hence the greater the mass and propulsion requirements of the vehicle. For example, a proposal for manned exploration of the planet Mars with a vehicle susceptible of production in the 1990's has an estimated total flight time (to and from Mars) for such a mission of approximately 1.5 years, with only a 20 day surface stay on Mars. A primary reason the duration of the surface stay is so short, is that the mass of onboard propellant necessary for a trip of such a range prohibits onboard storage of sufficient supplies for life-support systems and/or exploration vehicles needed for extensive exploration of the Martian surface beyond that 20 day stay.
A different proposal has been put forth for space exploration that minimizes requirements for onboard storage of propellants by providing for in situ generation of necessary propellants, as for example generation on the surface of Mars. The proposal is referred to by the phrase "Mars Direct", and is detailed in a publication by R. Zubrin, D. Baker and O. Gwynne entitled Mars Direct: A Simple, Robust, and Cost Effective Architecture for the Space Exploration Initiative, AIAA 91-0326, 29th Aerospace Sciences Meeting, Reno, Nev., January 1991, published in 1991 by the American Institute of Aeronautics and Astronautics (hereafter referred to for convenience as the "Zubrin Article"). The Zubrin Article is available to the public by writing to the Institute at 370 L'Enfant Promenade, S.W., Washington, D.C. 20024, and is hereby incorporated herein by reference, as it sets forth aspects of the working environment of the present invention.
In essence, Mars Direct calls for a launch of a first heavy lift booster rocket optimized for Earth escape to deliver to the Martian surface an unmanned and unfueled Earth Return Vehicle ("ERV"). While on the surface, the ERV will fill itself with methane and oxygen propellants generated primarily out of indigenous resources. After the propellant generation is completed, a second heavy lift booster rocket delivers a crew of human explorers to the site on the Martian surface of the ERV to use the generated and stored propellants for extending explorer life support system supplies; for powering exploration vehicles; and, for powering the ERV to deliver the crew back to Earth after an extensive surface stay of approximately 1.5 years. The Mars Direct Architecture also embraces an advantageous unmanned mission to sample Martian soil and/or atmosphere and to return accumulated samples to earth (a "sample return" mission). Such a mission would also benefit from generation of propellants from indigenous resources by minimizing onboard fuel storage requirements thereby enhancing storage capacity for sample access equipment and for samples to be returned to earth.
As detailed in pages 11-15 of the Zubrin Article, the processes for manufacture of propellants methane (CH.sub.4) and oxygen (O.sub.2) are well known in the art. The peculiarity of the Martian atmosphere that makes in situ production of those propellants practical, or especially coherent as part of the Mars Direct architecture for the Space Exploration Initiative, is that the atmosphere is composed of approximately 95.3% carbon dioxide (CO.sub.2). Known earth-based technology has for some time achieved conversion of CO.sub.2 to the propellant CH.sub.4 by the simple expedient of adding diatomic hydrogen (H.sub.2) to the CO.sub.2 in the presence of a catalyst such as nickel to produce the well known methanation, or "Sabatier" reaction (hereinafter referred to for convenience as the "Sabatier reaction", or "reaction 1") , which is: EQU CO.sub.2 +4H.sub.2 =CH.sub.4 +2H.sub.2 O (1)
The Sabatier reaction is exothermic, and will drive itself to produce methane and water (H.sub.2 O) at a rate that is dependent upon the supply of the reactants carbon dioxide and diatomic hydrogen. It has been in widespread commercial application for many years, wherein the reaction takes place in the presence of an appropriate catalyst housed in a "sabatier unit" examples of which are well known in the art.
As shown in a simplified fluid schematic drawing in FIG. 1, production of the second propellant, diatomic oxygen (O.sub.2), results from first separating the water from the methane, as for example by cooling the mixture of methane and water to condense the water and separating the liquid water from the gaseous methane in a common gravity phase separator, and second directing the water into an electrolyzer. In the electrolyzer, the familiar electrolysis reaction takes place (hereinafter referred to for convenience as the "electrolysis reaction" or "reaction 2"), which is: EQU 2H.sub.2 O=2H.sub.2 +O.sub.2 ( 2)
The diatomic hydrogen is then delivered back to the sabatier unit to supplement the original source of hydrogen, while the diatomic oxygen is stored. In the Mars Direct scenario, the ERV would run the aforesaid reaction based upon a stored supply of earth sourced diatomic hydrogen brought to the Martian surface in the ERV, while the carbon dioxide would be extracted directly from the Martian atmosphere, filtered and compressed into storage tanks in the ERV. The resulting methane and diatomic oxygen propellants would be separately stored so that the oxygen could oxidize the methane, and the oxygen could be used separately for life support systems, etc.
As is will known in the art, and as detailed in the Zubrin article at pages 11-15, a significant benefit of generating the methane and oxygen propellants on the Martian surface using atmospheric carbon dioxide is the "mass leverage" that can thereby be obtained for powering the ERV's rockets, and related exploration vehicles. "Mass leverage" refers to the mass of products produced compared to the mass of transported hydrogen. Through use of reactions 1 and 2 in the proposed ERV, a mass leverage of 12:1 can be obtained. It is that substantial advantage that affords the Mars Direct architecture opportunity for extensive surface stays on the Martian surface, as well as for long-range surface exploration through use of exploration vehicles powered by methane/oxygen based internal combustion engines. Such vehicles have a much more favorable power to mass ratio as opposed to exploration vehicles powered by known fuel cell or photovoltaic technology.
Consequently, in situ propellant generation enables Mars Direct to greatly enhance mission capability. In contrast, architectures for the Space Exploration Initiative that do not rely on propellant production based upon indigenous resources require that virtually all mission propellants for exploration and a return trip be stored onboard the exploration vehicle. For an endeavor comparable to a Mars Direct exploratory mission, such requirements would substantially increase the vehicle's size and/or complexity associated with earth orbital assembly; its propulsive requirements; and finally its total cost.
The known applications of reactions 1 and 2 satisfy requirements for generation of methane and oxygen propellants where the commercial applications involve a system that includes regular monitoring of the input rates of the reactants diatomic hydrogen and carbon dioxide and the output rates of the products methane and diatomic oxygen. Monitoring and adjusting those rates affords efficient use of the energy required for a sabatier unit, an electrolyzer and related system components (control valves, pumps, compressors, etc.), and also ensures that relative proportions of the two reactants are properly balanced so that neither is wasted. Additionally, known systems using reactions 1 and 2 are able to separate unreacted carbon dioxide and/or diatomic hydrogen from the stored methane or oxygen products. Additionally, commercial systems are able to quickly make adjustments for fluctuations in reaction and condensation rates of fluids resulting from ordinary fluid dynamics, as for example where the reactant gases are exposed to solid surfaces in the sabatier unit or electrolyzer, or at a gas/liquid phase interface in a condenser), Finally, known systems can also adjust for unforeseen interruptions in reactions 1 or 2, such as through failure of a portion of a sabatier unit or an electrolyzer, or an obstruction in any portion of such a system that effects input rates of the reactants, or output rates of the products.
The Mars Direct application of a system using reactions 1 and 2, however affords no opportunity for a technician to monitor and adjust rates of input and output of the reactants and products in the event of requirements for such adjustments. In particular, where a Mars Direct mission is relying upon a specific amount of stored propellants to return explorers to Earth in the ERV, it is absolutely critical that the propellants achieve a required specific impulse to return the ERV to earth. If the stored propellants, however contain more than trace amounts of unreacted carbon dioxide, diatomic hydrogen or water vapor, the level of performance of the propellants may be inadequate to achieve that specific impulse. Consequently, the rates of input of the reactants must be adjusted to compensate for ordinary fluid dynamics as well as for unforeseen interruptions in system components so that the stored, earth sourced hydrogen is not expended before the requisite product methane is produced; so that excessive carbon dioxide, water vapor and/or diatomic hydrogen is not stored with the propellants; and, so that unnecessary energy is not required to operate the electrolyzer, sabatier unit, and other required system components.
Accordingly, it is the general object of the present invention to provide a propellant generator that overcomes the problems of the prior art.
It is a more specific object to provide a propellant generator that affords automated control of rates of input of reactants into the generator.
It is another object to provide a propellant generator that affords a separate automated control for the rate of input of each reactant entering the generator.
The above and other advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.